
// Given a binary tree, each node has value 0 or 1.  Each root-to-leaf path 
// represents a binary number starting with the most significant bit.  
// For example, if the path is 0 -> 1 -> 1 -> 0 -> 1, then this could represent 01101 in binary, which is 13.

// For all leaves in the tree, consider the numbers represented by the path from the root to that leaf.

// Return the sum of these numbers.

//  